Researchers dig into the brain to resolve hearing loss

SAN JOSE, Calif. — Cochlear implants have long been the gold standard for providing profoundly deaf people a remedy to hearing loss.

The use of auditory brainstem implants is under clinical research in the U.S. and might be a future option for deaf infants and young children. | Photo Courtesy of Cochlear Inc.

However, not everyone qualifies for the procedure. About 100 children are born each year without a missing or malformed cochlear nerve, rendering them ineligible for the procedure.

Dr. Eric Wilkinson of the House Clinic and Huntington Medical Research Institutes and scientists at the Keck School of Medicine of the University of Southern California are digging deep into the brain in order to give those children a chance at audition.

A Los Angeles-based team of researchers — Wilkinson, Dr. Mark Schwartz, Dr. Laurie Eisenberg and Dr. Robert V. Shannon — are in the midst of a five-year safety and feasibility study, funded by the National Institutes of Health, that tests the costs and benefits of auditory brainstem implant use in infants and young children. It is the first phase in a longitudinal program that will test whether or not ABIs are a viable audiological device.

So far, four patients — three who were failed cochlear implant recipients and one who didn’t have a cochlear nerve — have received treatment through the study. They face a lengthy learning curve, but it is one that gives these children a chance they otherwise would never get.

According to the most recent data from the National Center for Birth Defects and Developmental Disabilities, 1.8 percent of infants do not pass hearing tests.

“We have to remember that these children are incredibly disadvantaged. Profound hearing loss is a very handicapping condition,” said Dr. Nan Ratner of the University of Maryland. “Most of the children who are born deaf do not live in a signing environment. Our basic job is to get as many ways of communication as quickly as possible.”

The ABI looks much like a cochlear implant, but with an extended stem that reaches deep into the brain. | Courtesy of Cochlear Inc.

A cochlear implant is basically an audio amplifier that bypasses the eardrum and uses electronic pulses to instigate action in the cochlear nerve, which is used to hear. The ABI is also uses electrodes to stimulate hearing, but it does so by using a conduit that goes much deeper into the brain and directly sends sound to the portion of the brain that interprets sound. It does not interact with the cochlear nerve.

Although ABI surgery has been offered in Europe since 2000, there has never been a formal, regulated safety and feasibility study done on the practice, let alone a look at the effects of it over longer periods of time, Eisenberg, a co-author on the study, said. That type of study is an integral part to earning FDA approval for young patients in the U.S., who might be especially viable as recipients because of the “plasticity” of their brains, as Shannon put it. Infants and young children are more malleable to change than adults, he said, and that means they can better adapt to such a significant change in their body’s hearing abilities.

And this 8-by-3 millimeter pod is a catalyst for a massive transformation.

The ABI has 21 electrodes that connect from the device to the portion of the brain where it is placed. | Courtesy of Cochlear Inc.

“The brain can do powerful pattern recognition even when given highly degraded sensory information,” he said. “With a cochlear implant and a retinal implant, the information is arrayed across the sensory organ much in the way it normally would be, like this picture.”

Because their brains haven’t been trained to understand noises, ABI patients get a different picture at first: one of Lincoln, but with the pixels thrown about to different places — the nose where the throat should be, for example, or the head turned upside-down — which make it more difficult, or altogether impossible, to conceptualize the picture. The brain has to be trained to put those pixels in the right order.

“Initial activation of the ABI device in a congenitally deaf child is analogous to a newborn hearing for the first time,” Eisenberg said. In other words, a 3-year-old who receives the operation won’t hear like a 3-year old. “She’ll be hearing like a newborn. … Her hearing age is that one day old.

“The children with ABIs require intensive long-term therapy and very strong family involvement.”

Training includes working with pronunciation, association of sounds to objects and colors and other common tasks given to infants. There’s no quick fix for profound loss of hearing because of malformations.

“It’s a myth to assume that the device goes in, and the kid starts being able to figure out sounds,” Ratner said. “The notion that the device does it all has never been correct. What’s happening over time is children are pulling in multiple forms of information to unscramble that sound.”

Insertion of the ABI is also controversial and of inherent risk.

Any work with the brain, particularly in children, is highly scrutinized. This procedure is a deep, intrusive operation that requires a high degree of expertise.

In the U.S., because of FDA regulations, only persons 12 or older with neurofibromatosis type II, which causes brain tumors on the hearing nerves, can get ABIs. The researchers received an exemption in order to run clinical trials on their younger patients.

The FDA, the NIH and various institutional review boards vetted and approved the protocols of the study.

“There is potentially a downside. We have high hopes and certainly don’t expect anything bad to happen, but I can’t say that’s not a possibility,” Schwartz said. “Also, there’s a high degree of technical proficiency and precision that’s needed. It’s my understanding and my experience that this is a very precise operation that really requires exacting technique to maximize benefits. It’s very easy, not so much in terms of the complications, but it’s very easy to injure the brain, which could influence results.”

Despite the obstacles, the benefits of ABIs might be tremendous. Anecdotal evidence from current participants suggests the devices are working “very well,” the researchers said, but the trials are progressing on a steady and cautious timeline. Schwartz said any hasty conclusions might be detrimental.

“There are some patients that are doing very well,” in these trials and others, Schwartz said, “but that’s not the full picture.”